Process for refining alloys of lead and tin



Patented Nov. 24,- 1936 UNITED STATES PROCESS FOR Mme ALLOYS F LEAD AND TIN Jesse 0. Betterton and Yuril E. Lebedeff, Metuchen, N. J.. assignors to American Smelting and Refining Company, New York, N. Y., a corporation of New Jersey No Drawing. Application August 27, 1935, Serial No. 38,060

12 Claims.

This invention relates to the treatment of leadtin alloys and provides a process for readily purifying or refining such alloys with respect to such impurities as arsenic and copper and, more par- 6 ticularly, antimony and silver.

The refining of lead-tin or white metal alloys presents a serious problem from the economic standpoint because of the dificulty in eliminating the impurities associated with the alloy without 10 sacrificing prohibitive quantities of lead and tin.

As will be observed from the description, the present invention provides for the removal of the impurities within the limits of market tolerance in a highly efiicient manner without the loss of abnormally high quantities of the lead-tin alloy itself.

In general the invention contemplates first treating the lead-tin alloy with zinc thereby substantially eliminating such impurities as arsenic and copper and materially reducing the anti-.- mony and silver contents and thereafter treating the alloy with such an alloy of magnesium as will further reduce the antimony and silver contents yielding a marketable lead-tin alloy. In some particular instances, depending upon the kinds of impurities and the amounts thereof present in the metal treated, it may be possible to dispense with the first treatment.

While various details of operation may be varied somewhat as will appear from the specific examples hereinafter given, the invention may be practised by melting the impure solder or other lead-tin alloy in an ordinary cast iron refining kettle and the initial refining accomplished by incorporating zinc in the melt by means of a mechanical mixer, the impurities being removed as drosses and/or crusts after being appropriately pressed. An appropriate alloy of magnesium, preferably magnesium-aluminum or magnesiumzinc, is then introduced into the partially refined alloy with the formation of dresses and/or crusts containing further quantities of the impurities. These drosses and/or crusts are likewise pressed Ztoextract entrained metal which is returned to the bath. In order to eifect as complete a removal of impurities as is possible, the bath is finally liquated ,to substantially freezing temperature, the dross and crusts obtained thereby being appropriately used in the treatment of additional quantities of impure lead-tin alloy. The invention is perhaps better illustrated-by the following specific examples, the first being directed to the initial treatment of impure leadtin alloy with zinc and the subsequent examples to the subsequent treatment with magnesium alloys.

Example 1 A typical lead-tin alloy contaminated with antimony, arsenic, copper, nickel, gold and silver in amounts shown in the table below was melted in a cast iron refining kettle, the melting dross skimmed and the bath heated to 850 F. To 117.9 parts by weight of the bath, 10.1 parts by weight of metallic zinc were added and the entire charge mixed for one-half hour with a mechanical mixer within a temperature range of 880 F. to 840 F. The mixer was then withdrawn, the bath cooled to 820 F. and 19.8 parts by weight of pressed dross removed. The bath was further cooled to 560 F. and anadditional 15.8 parts by weight of pressed dross removed after which the bath was cooled to substantially freezing and 15.1 parts by weight of dross removed. The bath, 77.3 parts by weight, was sampled and analyzed as shown under intermediate metal in the table below.

To 70.2 parts by weight of the intermediate metal, 3.4 parts of zinc were added at approximately 850 F. and the bath mixed for fifteen .minutes within a temperature range of 850 F. to 810 F. after which the mixer was again removed, the bath cooled to about 560 F. and pressed dross amounting to 3.6 parts by weight removed. The bath was then cooled to substantially its freezing point at which time 9.9 parts by weight of dross were removed and the final bath of 60.1 parts by weight analyzed as shown in the table:

Inter- Percent Original Final (Au, Ag-ozJ'l) metal figgf metal Sb 12. 31 5. 13 1. 45 As 1.02 Trace None Cu 1. 3 0. 009 Trace Pb 45. 4 51. 7 52.01 Ni 0. 17 0.012 Sn 39. 6 42. 8 43. 86 Zn None 0.39 2. Au 0.01 None None Ag ll. 5 12. 0 4. 4

In this instance, 133.7 parts by weight of solder which had previously been treated with zinc was melted, the melting dross comprising one and one-half parts by weight skimmed and one part by weight of magnesium-zinc alloy analyzing 50.2% Mg and 19.8% Zn stirred into the bath at a from approximately 610 F. to approximately 625 F. with a mechanical stirrer. The alloy dissolved readily after about eight minutes of mixing at approximately 620 F.

Percent 1 2 3 Sb 1. 51 0. l3 0. 08 As None None None Cu Trace None None Pb 43. 9 44. 9 45. 2 Sn. 51. 6 52. 51. 8 Zn 2. 9 2. 9 2. 9 Mg None 0. 060 0. 049

It will be noted that the antimony content was reduced from 1.51% to only 0.08%. Based on the formation of the compound MgsSbz this .shows an efi'iciency of 128% calculated upon the basis of magnesium above, the zinc accounting for the excess.

For purposes of comparison a sample of impure solder but which contained no zinc was treated with magnesium metal turnings at a temperature of 625 F., 78 parts by weight of metal and 0.5 part by weight of magnesium metal turnings being used. It required approximately two and one-half hours of stirring to eifect solution of the magnesium and then the antimony content was only decreased from 1.74% to 1.21% which represents an efliciency of only 40.6% on the basis of magnesium. In a similar test on zinc free solder but using magnesium-zinc alloy comprising approximately 50% of each element an efiiciency of approximately 90% on the basis of the magnesium was readily obtained in spite of the fact the first hour of mixing was performed at from 560 F. to 580 F. which was conducive to adverse oxidation of the alloy before incorporation.

Example 3 Solder previously treated withzinc was melted .and the melting dross skimmed. To 144.1 parts drosses and final metal were:

Original First Second Final Percent metal dross dross metal Sb 1. 5 19. 8 2. 4 0. 08 Pb 43. 6 25. 7 41. 1 44. 6 Sn 51. 0 34: 3 51. 5 51. 5 Zn 3. 64 11. 4 4. 6 3. 6 Mg None 5. 9 0. l 0. 086

This run showed an efliciency of magnesium with respect to antimony removal in the dross of 100.03% to which the zinc contributed. A parallel test on solder containing no zinc and using magnesium alone showed a magnesium efficiency of only 78.7% and even at 800 F. it re- 9,061,994 The dross formed was removed and comprised quired substantially twice as long a mixing period to eifect solution of the reactant.

Example 4 One hundred twenty-four and. three-tenth by Weight of solder which had previously been treated with zinc was melted in an open kettle and the melting dross amounting to three and three-tenths part byweight skimmed from thebath. To the remaining 121 parts by weight 0.48 part by weight of magnesium-aluminum alloy analyzing 50.3% Mg and.49.7% Al was added at approximately 820 F., the alloy going into solution upon two minutes of stirring. The resulting dross was skimmed and pressed, 17.8 parts by weight being removed at about 800 F. The bath was cooled to approximately 500 F. and 5.3 parts by weight of dross removed and thereafter the bath was cooled to freezing and 3.5 parts by weight removed. The final bath, 94.9 parts by weight was reheated to 500F. and sampled. Analyses were as follows:

Original After Per- After first Fmal melted second cent m etal skimming skimming metal Sb 1. 4 0. 35 0. 06 0. 04 Pb 59. 5 60. 8 60. 8 62. 3 Sn 36. 5 36. 3 36. 6 35. 6 Zn 2. 5 2. 5 2. 5 2. 0 Mg None 0. 080 0. 046 0. 042

Of the drosses the first contained 7.53% Sb, 0.9% Mg and 2.5% Zn while the second showed 5.7% Sb, 0.7% Mg and 2.5% Zn.

It will be noticed that with the magnesiumaluminum alloy the antimony was reduced to 0.04% and that the efliciency of antimony removal calculated on the basis of magnesium was 252%.

Example 5 To 148.8 parts by weight of skimmed, melted down solder containing silver which had previously been refined with zinc, 6.1 parts by weight of magnesium-zinc alloy (10% Mg, 90% Zn) were added and the bath skimmed (24.3 parts by weight) at 800 F. The bath was cooled to freez ing and crusts and dross amounting to 44.3 parts by weight were removed. The bath (86.3 parts by weight) was then heated to 600 F. and sam-- pled. Analyses of the original and final baths were:

Percent Original Final (Agozs./T) bath bath Sb 1. 0 0. 05 Pb 60. 0 60. 8 Sn 36. 3 36. 0 Zn 2. 5 3. 0 Ag 8. 4 0. 2

It will be readily apparent from the foregoing examples that the present invention effects definite improvements in the refining of lead-tin alloys. Thus the results clearly show that a much higher efilciency is obtained using appropriate alloys of magnesium than when magnesium is employed alone. Preferably zinc or aluminum will constitute the metal alloyed with the magnesium but other alloying metals such as lead and tin may be used. For example, an efficiency of 82.3% relative to antimony removal was obtained using an alloy comprising 60.6% magnesium and 39.3% lead on solder containing 1.61% antimony. Also, the magnesium may be used in the form of ternary alloy such as magnesium-aluminum-zinc if desired.

It. may also be noted that any residualreagents such as zinc, magnesium, aluminum, etc.

remaining in the final metal are readily removed by simple oxidation or chloridization treatments as ordinarily practised.

V of impurities.

Various modes of operation will suggest them selves to those skilled in the art. For example,

in the case of a lead alloy or tin alloy conta'ining only relatively small quantities of impurities- (arsenic, antimony, copper, silver, etc.) t'he treatment with zinc may be eliminated orsmall amounts of zinc added to the metal. However,

in any event, it will be found that theuse'of magnesium in alloy form-renders a decidedly higher removal efliciency than'the use of the metal itself alone.

What is claimed is:

1. The process for refining impure solder which comprises establishing a bath of the "impure solder, incorporating zinc therein and effecting" a partial separation of impurities, and incorporatng magnesium'in alloy form in the remaining metal thereby effecting a-iurther separation 2. The. process for refining a lead tin alloy containing such elements as arsenic, antimony, copper and silver which comprises first treating a bath of the alloy with zinc, separating drossesand crusts therefrom and then'treating the bath with a suitable alloy of magnesium and separating the resulting drosses and/or crusts-from the refined alloy.

' 3. The process for treating lead and tin'containlng relative large amounts of antimony which comprises incorporating zinc.

' into the alloy to remove a portion of the antimony and afterward incorporating an alloy of magnesium alloy and the impure metal and efleoting nesium into the alloy to remove further quantities .of antimony.

4. The process for reflning alloys oi." lead and tin containing antimony as- ,an impurity whichcomprises establishing a molten bath thereof, incorporating therein an alloy of magnesium with aluminum or zinc and which may also contain lead or tin, causing a dross to form-in which the antimony. content oi the bath isiconcentrated and separating the dross from the bath. T v

5. The process for refining impure solder metal which comprises melting the impure metal in the presence of a reactant -comprising efiective amounts of magnesium alloyedwith aluminum or zinc, producing a reaction between the'magan impure alloy of refined solder.

a separation oi. resulting reaction products containing the impurities from the bath.

6. The process for refining impure solder metalwhich comprises melting the impure metal in the .presence of relatively-small quantities of zinc. adding a reactant alloy containing magnesium in. efiective amounts, producing a reaction between the magnesium :alloy and'the impure metal and.

separating the-resulting reaction products containing the impurities from the bath.

ing a reaction between thealloy and the impure metal and separating the resulting reaction products containing impurities from the bath.-

8. The process for separating impurities in- I eluding antimony from solder metal containing 10 w "l.- The process for refining impure solder metal which comprises meltingthe impure metal inv the presence of a magnesium-zinc alloy, produc-.

the same which comprises incorporating a magnesium-zinc alloy in a molten bath of the solder metal and removing the resulting'dross from the bath of metal, the said dross having the impurities, includ ing antimony, concentrated therein.

9. The process for separating impurities in- :cluding antimony from solder metal containing the same which comprises incorporating a mag-. nesium-aluminum alloy in a molten bath of the solder metal and removing thefresultin'g dross I I irom' thesaid bath, in which dross thesaid im--- purities, including antimony, are concentrated.

10. The process for refining solder which comprises incorporating an alloy of magnesium 'andaluminum or zinc containing suflicient mag pressing the said dross and cooling-the said bath to freezing while separating cooling dross there- 'Irom as produced. 4

12.. The process fortreating-antimony-bearing solder metal which comprises reacting a molten bath thereof with magnesium in the presence of zinc, cooling the bath and separating the'dross' in which the antimony is concentrated from the JESSE, o. BE'I'I'ERTON." YURlI nrnnrznm; 

